Specific data on errors, near misses, and adverse events occurring during emergency medical services (EMS) care do not exist. The recent Institute of Medicine report on medical error found emergency medicine (EM) to have the highest rate of preventable adverse events among the medical specialties. Although prehospital medical care has not been studied, it is reasonable to expect that EMS, which is similar to EM and has even more of the characteristics that are known to place EM at high risk for error, also has a high rate of adverse events. Moreover, 25 million patients receive EMS care annually in the US, so that the exposure of the US public to risk of medical error in this environment is substantial. Eliminating adverse events must be a priority for EMS systems to ensure quality medical care. To improve patient safety in EMS a clear understanding of the nature of the medical errors, near misses, and adverse events that occur in EMS must be developed. Real-time event reporting systems represent one proven and effective means of acquiring information about such events in a rapid and reliable fashion. Use of a reporting system modeled after the successful Aviation Safety Reporting System (ASRS) has been demonstrated to be effective in this role in non-aviation, health-related settings including Veterans' Administration (VA) hospitals. Several commercial event reporting systems for hospitals have become very successful. None of these systems satisfy the unique needs of EMS, but they serve as evidence that there is a need for commercial systems and potential for commercial success. The Medical Error Prevention and Reporting System (MEPARS) is the only known commercial error reporting system designed on the principles of the ASRS and targeted for EMS. A local, agency-specific version of MEPARS has been pilot tested at one EMS agency, with notable successes in identifying and eliminating errors. The overall objective of the proposed Phase I project is to refine and expand MEPARS and test its feasibility by implementing the system in a large urban/suburban EMS system. At the conclusion of this project, an infrastructure will be in place that will allow the MEPARS system to easily be implemented nationwide. The resulting database will allow researchers to gain a better understanding of the nature of medical error in EMS, and thus design interventions and system changes to minimize adverse events as a result of these errors.